The push toward smaller and faster semiconductor devices has resulted in a shift towards the use of copper for making electrical interconnections in integrated circuits. For instance, copper offers a number of benefits over aluminum: higher electrical conductivity, good resistance to electro-migration, and reduced cross talk and propagation delays at higher interconnect densities. Copper interconnects are not without difficulties, however. For instance, copper atoms readily diffuse into silicon-containing dielectric layers, with resultant degradation in the performance of active devices in the integrated circuit. It is therefore necessary to dispose a barrier layer between a copper interconnect and the dielectric layer to decrease the diffusion of copper into the dielectric layer.
The requirement for a diffusion barrier layer when using copper-containing interconnects introduces another problem. Because the barrier layer occupies a portion of the space in the interconnect, the thickness of the copper layer deposited over the barrier layer in the interconnect is reduced. A thinner copper layer results in an increase in the resistance across the interconnect, which in turn, results in slower active devices. It is desirable therefore to make thin uniform diffusion barrier layers. The need for a thin uniform barrier becomes increasingly important for each reduction in each technology node size.
It has proven difficult, however, using conventional methods to produce barrier layers that uniformly and conformally coat the interconnect. Consequently, when filled with copper, there are regions of sidewall where the thickness of copper is small because of a thicker barrier layer thereunder, thereby increasing resistance and slowing the active device. In addition, the performance of active devices containing such an interconnect may be compromised because copper atoms can diffuse into the dielectric layer through portions of the sidewall that are not coated with, or have areas with too thin a barrier layer. Moreover, because the uniformity of the barrier layer can vary widely from center to edge of a wafer, the device performance of similar devices built on different areas of the same wafer can vary considerably from each other.
Accordingly, what is needed in the art is a method and system for manufacturing copper interconnects having uniformly conformal, thin, and continuous interconnect barrier layers, while avoiding the above-discussed disadvantages associated with conventional methods and systems for forming barrier layers.